Honda GX31
08-12-2005, 03:07 AM
#26
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RE: Honda GX31
ORIGINAL: av8tor1977
In the diagram that I posted, it doesn't show a one way trap valve in the drain back from the valve train area to the sump tank, but there must be one since Honda says it can be run inverted.
AV8TOR
In the diagram that I posted, it doesn't show a one way trap valve in the drain back from the valve train area to the sump tank, but there must be one since Honda says it can be run inverted.
AV8TOR
That's right, I thought you meant oil draining into the crankcase from the tank, sorry. - It wouldn't make a lot of sense not to have one at the return end! - don't think it would matter so much when it's running, but stored upside down it wouldn't be too good.
08-12-2005, 03:26 AM
#27
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RE: Honda GX31
More information "close to the vest" 
Update on the Shindaiwa 34cc.....Stock WYL carb, 18-6 Mejzlik, 7500 rpm..Larger WYL carb, 8000 rpm..
There's a reed valve on the bottom of the case and another between the carb insulator block and the cylinder...Runs great, just no needles on the stock WYL series carb...I didn't try to use a stock 2 cycle carb on this one...
The Stihl 64.9 turns a 24-8 PK prop 6200 with the stock non adjustalbe carb halfway choked..
A Walbro SDC 80 works good on it, using the stock crankcase pulse fitting connected to the back of the carb...Don't see any reed valves at all on this one..
It has a mechanism built in to the cam somehow to just barely bump the valves open before the piston reaches TDC, probably to release some of the compression for easier starting...The result of this is fuel pushed back out the carb like a ported 2 stroke...
The Shindaiwa is timed at 28 BTDC with no syncro, tried it both ways and can't see any difference..
The Stihl has a syncro module in it, set to reach full advance at 6000 rpm and idle with 26 degrees retard at 1500 rpm...
I have converted 4 of the Stihls, 2 with stock mag to run CCW and 2 with CD ignition to run CW....The mag engines won't hand start and the way the case is made the mount is not as strong.....
I found a few 15 mm WYJ carbs that have adjustable needles. They would probably be good if not for the strong return spring..It can't be removed because the inner rotor raises up as the throttle is opened to change the mixture, and without the spring it would just float around...
Update on the Shindaiwa 34cc.....Stock WYL carb, 18-6 Mejzlik, 7500 rpm..Larger WYL carb, 8000 rpm..There's a reed valve on the bottom of the case and another between the carb insulator block and the cylinder...Runs great, just no needles on the stock WYL series carb...I didn't try to use a stock 2 cycle carb on this one...
The Stihl 64.9 turns a 24-8 PK prop 6200 with the stock non adjustalbe carb halfway choked..
A Walbro SDC 80 works good on it, using the stock crankcase pulse fitting connected to the back of the carb...Don't see any reed valves at all on this one..
It has a mechanism built in to the cam somehow to just barely bump the valves open before the piston reaches TDC, probably to release some of the compression for easier starting...The result of this is fuel pushed back out the carb like a ported 2 stroke...
The Shindaiwa is timed at 28 BTDC with no syncro, tried it both ways and can't see any difference..
The Stihl has a syncro module in it, set to reach full advance at 6000 rpm and idle with 26 degrees retard at 1500 rpm...
I have converted 4 of the Stihls, 2 with stock mag to run CCW and 2 with CD ignition to run CW....The mag engines won't hand start and the way the case is made the mount is not as strong.....
I found a few 15 mm WYJ carbs that have adjustable needles. They would probably be good if not for the strong return spring..It can't be removed because the inner rotor raises up as the throttle is opened to change the mixture, and without the spring it would just float around...
08-12-2005, 08:16 AM
#28
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RE: Honda GX31
The oil draining is just the film of oil that is circulating through engine. The "trap door" is a reed valve in the crankcase.
The oil in the oil tank can't make it out of it with out getting whipped into a mist and sucked into the crankcase.
The return passage enters the tank in the center , as long as the the oil level is at the proper amount (not overfull) oil won't drain out.
Honda says it can be stored in any postion also , but experience shows that a few drops of oil may come out of the breather tube.
I have seen a few of these engines apart at a friends shop and had a first hand tour of the inside workings.
Some guys get around the return spring problem by cutting off the hook on the spring , so it no longer has radial tension , but leaving it in place to pull the "rotor" down on the ramp.
The oil in the oil tank can't make it out of it with out getting whipped into a mist and sucked into the crankcase.
The return passage enters the tank in the center , as long as the the oil level is at the proper amount (not overfull) oil won't drain out.
Honda says it can be stored in any postion also , but experience shows that a few drops of oil may come out of the breather tube.
I have seen a few of these engines apart at a friends shop and had a first hand tour of the inside workings.
I found a few 15 mm WYJ carbs that have adjustable needles. They would probably be good if not for the strong return spring..It can't be removed because the inner rotor raises up as the throttle is opened to change the mixture, and without the spring it would just float around...
08-13-2005, 12:48 AM
#29
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RE: Honda GX31
Inverted 4c in airplanes is OLD stuff... Check out the Ranger engine in the PT-19. If you really want to see it done right , check out the DB 601 used in the Me109, 12 cylinder inverted V.
08-14-2005, 09:51 AM
#30
RE: Honda GX31
OK, after looking at it real hard, I decided the Dynaflite Decathlon was not ideal for the engine. A great plane, but just too little wing and too much weight. So I bit the bullet and plunked down the money for a Rascal 110. It arrived this week and is a great match for the GX31 in terms of wing area and weight. From the reports of how well it flies on a 25cc 2 stroke (about the same power as the GX31) it should be fine with the extra Lb or two on those giant barn door wings. I am moving at the end of the month but I should be able to have it up for a test flight by the end of Sept. The battery, servos and reciever are all probably going to the tail. The only negative so far is that the Cowl is totally useless. I could see a round cowl but I don't know how it would look on a slab side. I know I saw a full sized aircraft that was slab sided with a radial that had one and it didn't look too bad. Any suggestions on a cowel? The oil tank is only a MM or so larger than the firewall and the major problem is the oil filler, carb etc. that sticks out, then that flywheel/mag up front.
08-29-2005, 07:23 PM
#31
RE: Honda GX31
Check out this thread, tward the end. He converted and has been flying his at a local field. The sound is amazing and there seems to be plenty of power, inverted.
http://www.rcuniverse.com/forum/upfi...42/Id97850.jpg
http://www.rcuniverse.com/forum/upfi...42/Id97850.jpg
